War, or its prospect, forces decisions and divisions which are deeper than those of peacetime. The decisions which must be made concern lives: not, now, just those of the military who are commanded to risk them, but of the many more civilians who are at risk from modern wars, and who are the prime targets of modern terror.

The question of war "is it worthwhile?" is always a good one. The left, for good democratic reasons, has always asked it more urgently than the right. In most countries, the right retains a residual sense of military necessity and military honour: the necessity of going to war to gain security of the state by deterring its present or future enemies, and the honour which commits the military, unquestioning, to fulfil these demands by the state.

The left has a long tradition of pacifism. Some of that was ethical or religious, and thus not confined to the left. More of it has come from the historic base of the movements of the left, created from those sections of the population who suffered most from modern wars: the poor who were bombed or shelled in greater numbers, and the poor who were conscripted and died in large numbers, and who had had little direct say in the decisions leading up to war's declaration.

But the dilemmas of modern war and terror are not so ideologically tidy. Individualism - more of a right wing cause than a left wing one - privileges choice and the enhancement of life. Making choices conflicts directly with obedience and honour, which have been the implicit bases of the armed forces. The mass can no longer be treated as a mass, and is not to be mobilised by mass appeals from either right or left.

The left has also had a stronger and more cherished tradition of anti-fascism. It was the left in Germany and in Italy which most fiercely opposed fascism (though it was also sections of the left which helped to create it). The left in Europe mobilised international resistance to the Nationalist forces in Spain during the civil war, and called for their states to intervene on the republican government's side.

These traditions - of pacifism, individualism and anti-fascism now meet another: anti-Americanism, not confined to the left in developed states, but most virulent on it. Inspired by powerful (among the young) prophets as Professor Noam Chomsky, sharpened by the anti-globalisation movement which tends to equate America with capitalism, the emotive force of opposition to the global superpower was gathering strength before September 11: and, ironically, has continued to gather force after it.

Some definitions are needed, particularly for those Americans who attend to European debates. Anti-Americanism is not criticism of the American government's policies, any more than criticism of the Israeli government's policies is anti-Semitism. But there is now a narrative of the left - complete in itself in the way such narratives are - which sees in the US an imperial predator whose actions - all actions - are conditioned by this aspect of its being.

This narrative has ceased to be critical, but become predestinarian: rather as predestinarians divided humanity into those whose actions could never be wrong and those whose actions could never be right, so this strain of left critique arrogates to itself the first and confers on the US the second. It is important not to confuse this grand, totalising critique with criticism, from left or right. The latter is essential for governments, most essential for governments with such awful power as the US commands. But the totalising critique is an intellectual construct, derived from the techniques of 19th century philosophy, which bends all facts to fit the ideological line.

These issues lie behind the deepening cleavage on the British left. The creation of New Labour eight years ago, its assumption of power, its domination of the British political scene, have been accomplished at the cost of a deepening alienation of the left - especially of the intelligentsia. Tony Blair has little support on which he can count within the Academy, and less and less in the upmarket media. Left and right tend to join on an essentially cultural critique of New Labour as a formation devoid of historical depth, obsessed with spin, casual with the truth and - where bending towards the right for some of their policies - too flabby or cowardly to take on their own constituencies sufficiently to deliver the hazy promise.

The anti-Americanism, of that left which regards itself as keeper of a true socialism which New Labour has discarded, sees New Labour as a mere poodle of the US President, unable to articulate real British interests because of the posture Blair has taken. It takes heart from the opinion polls which show the British - as most Europeans - reluctant to countenance military action on Iraq: and demands proof of the involvement of the Iraqi regime in the September 11 bombing. It takes encouragement from a recent report by the UK Joint Intelligence Committee whose leaked conclusions are said to show no such link can be established.

It may be there is no such link: it is unlikely that it would ever be definitively proven. The modalities of any military action against Iraq need careful, and public discussion. But the view, which the far left in Europe powerfully expresses, that in a consideration of action against Iraq the folly, imperialism and crimes of America are the only matter which may enter the discussion is an abdication of the left's own attachment to enlightenment rationalism.

It also abandons, or at least suppresses, its own anti-fascist credentials. Osama bin Laden's al -Qaeda are murderous on a grand scale, as is Saddam's government; who have been especially murderous to those groups within Iraq - especially the Kurds - considered disloyal to his rule. He has shown willingness to invade neighbouring states, and to acquire weapons of mass destruction of all types - nuclear, biological and chemical. He is committed to destroying the Israeli state, and has sponsored terrorism against it and others.

It is neither folly nor imperialism to discuss how he might be deposed, and what assistance we might give to the Iraqi opposition to replace him. The question - is it worth it? - is a large part of such consideration. But the automatic assumption that it can never be - indeed, that the mere thought of it is a sign of evil intent - is, preposterously, the reflex of a substantial part of Europe's left intelligentsia.

The centre-left has a distinct, if under-developed view. It is that the processes of globalisation must be counterweighted with forms of global governance and justice which can bring the modern fascists to some kind of account - as Slobodan Milosevic, the former President of Yugoslavia, is presently being held to account in the Hague. The US, to date, has recoiled from such an attempt: and does so still. It must come round to them: or it stands exposed in a world where even its giant's strength requires alliances with the lesser nations who share its democratic and libertarian ideals.

· John Lloyd is a freelance writer and former editor of the New Statesman.